Composition for selectively removing top coatings



29 rately applied layers or coats tion, for example the top coat may Patented Oct. 25, 1932 UNITED STATES PATENT OFFICE BORIS N. LOU'GOVOY, F MONTCLAIR, JERSEY, ASSIGNOR TO CHADELOID CI HEII- CAL COMPANY, OF NEW YORK, N. Y., A. CORPORATION OF WEST VIRGINIA.

COMPOSITION FOR SELECTIVELY REMOVING- TOP COATINGS No Drawing.

character substantially unaltered and especially relates to a removing composition which will soften coatings of nitrocellulose lacquer leaving the undercoat unattacked and V also includes the process of selective removal, 19 as will be more fully hereinafter described.

The invention further embraces a process of accomplishing the removal of only an upper coat of one kind of finish, by a remover as contemplated herein, while leaving an undercoat y of a different character substantially untouched, and in a condition adapted to be recoated. I note in connection with the term coat as used herein, that this term is intended to cover oneor a plurality of sepa- (as the term 1s used by painters), of substantially' like (or at least related) com osibeen applied, for example, b one or several successive applications 0 a nitrocellulose' lacquer, carrying pigment or color, followed by one or. more successive applications of nitrocellulose lacquer not carrying pigmenta I 3o 7 In present day practice, particularly in the automobile refinishing trade, it is often desirable to remove only the outside coating of aint. Automobile bodies, especially of the ow price makes, frequently are first finished '35 with a'"co.at of baked enamel which after- 40 the baked enamel undercoat untouched and to apply a fresh coat of paint on the old undercoat of baked enamel.

Paint and varnish removers of the type most widely used are composed of mixtures of light solvents such as benzol and acetone Application filed July 21,

ave

1928. Serial No. 294,590.

(or benzol, acetone and alcohol) with a few per cent of wax incorporated in the mixture. A remover of this type will penetrate the nitrocellulose layer and will even attack the baked enamel undercoat, if left in contact with it for a considerable period, a condition which might at any time occur in practice. Although by such a treatment the baked enamel undercoat may not be softened clear through to the wood or metal, nevertheless the surface of such undercoat would be blemished and will require extensive treatment to permit ofrefinishing. According to the pres ent invention a remover is used containlng a selective. solvent or solvents which wouldnot act on the undercoat to soften it, even if left in contact with it for a considerable period oftime. I 4

It is also known that hydrocarbon solvents such as benzol or petroleum hydrocarbons in a paint and varnish removing com osition are usually necessary as a means to issolve the evaporation retarding constituent,-

such as. a Waxy body. When an appropriate proportion of solvent-which does not dissolve wax isl added to a solution of wax in such a hydrocarbon, the wax is precipitated in a peculiar gelantinized form forming a skin (or film) on the surface which acts as a retarder of the evaporation of the solvents.

The'addition of a non-hydrocarbon, wax non- (solvent which has good loosening properties, to a paint remover is necessary not only for the purpose of producingth'e formation of the above-mentioned wax film but also is necessary to obtain good efiiciency of the solvent mixture, because in general the hydrocarbons themselves are good penetrating solvents but do not possess good loosening power on dried paint. While this is true for all kinds of paint and varnish remover compositions containing hydrocarbons, it'is especially importent with such an inactive solvent of. dried aint as petroleum hydrocarbon. In this case 1t is particularly important to havea loosening solvent of the most powerful nature. In general the solvents possessing the greater loosening power are the solvents of low boiling point, i. e., of great volatility such as ace- .tone, methyl acetone and the like.

time. The rate of evaporation of a paint and 20 varnish remover depends not only on the amount and kind of wax or other evaporation retarding substance, but also on the volatility of wax solvents used and on the ratio between the volatility of a wax-solvent and the waxprecipitant used in conjunction with that solvent. In order to obtain a satisfactory low rate of evaporation the volatility of the waxprecipitant should be at least near or higher than the volatility of the wax-solvent used.

Petroleum hydrocarbons in paint and varnigh removers in addition to sluggish action or complete inaction, in most cases also pos sess the disadvantage of poor miscibility with other solvents, such as alcohols or ketones. The higher the boiling point range of the petroleum hydrocarbons the more easily they separate from admixture with other solvents of the prefered type. This is especially true in the presence of wax, which experiments have shown to considerably alter the miscibility equilibrium. Hence in many cases good miscibility can be obtained only with very low boiling, hence unduly volatile petroleum distillate.

An important consideration in connection with removers of these types, is the ability of the remover to remain wet (and active) for .40

a substantial period. To determine the relative rates of evaporation, comparative tests were made by exposing a layer of the respective composition, 7 m. m. deep, to free contact with the atmosphere at 72 to 75 F., in an open dish, and noting the percentage loss of weight in each sample at 30, 60 and 120 minutes. Six samples were treated, as given below, in the form of a table.

In Experiment 1, I used petroleum ether (B. P. 40 to 60 (3.).

In Experiment 2, I used petroleum naphtha (B. P. 60 to (1).

In Experiment 3, I used petroleum naphtha (B. R60 to 115 (3.). C n Experiment 4, I used benzol (B. P. 80

Experiment 5, I used toluol (B. P. 111 C.

In Experiment 6, I used xylol P. 149

The complete remover in each case was (by volume) 2 parts of the respective hydrocarbon, 1 part of anhydrous methyl alcohol and 1 part anhydrous acetone, and in all cases 2% of wax. The details of the experiments were all alike.

Loss by evaporation from the complete remover by weight) Time (minutes) Experiment No.

It will be seen thatthe rates of evaporation of N o. 1 and No. 4 are very satisfactory.

In order to produce a satisfactory remover using preferred loosening solvents and containing petroleum-hydrocarbons, the lightest fractions thereof should therefore be select-- ed. Numerous tests'have shown that such a fraction would be of the nature of petroleum. other.

Theuse of petroleum ether (in addition to and highly effective loosening solvents, is

used, the difficulty of securing a low rate of evaporation will immediately arise. In order p to reduce the rate of evaporation to a point acceptable for extreme service conditions, that is, so that remover will not lose more than five per cent of its weight in twenty-four hours when exposed to the atmosphere in an open dish under the conditions above specified. In making the remover I introduce into the wax-precipitant some component solvent possessing wax-precipitating roperties and having a voltility below that o the petroleum distillate. Such solvent may be a ketone such as methyl ethyl ketone, mesityl oxide, lugosol (condensation products obtained from acetone by treating with a small amount of alkali and. fractionally distilling to collect separately a fraction distilling between about 60 (1., and about 170 0., as covered in a copending application 280,955 filed May 26, 1928), aswell as solvents of an esteric nature. a

Solvents of this character which are to be added to the petroleum fraction for the purpose of the present invention preferably should be those which have a high cutting action on nitrocellulose coatings (lacquers) but yet must be without any substantial cutting action upon baked enamel.

Acetone being one of the most active for the purpose would, however, in addition to its high volatility, have the disadvantage of having a comparatively strong action on baked enamel if allowed to remain in contact with it for a long time and it is therefore preferable to use such solvent only in admixture with less powerful solvent, such as tion of a highly active solvent only with reference to the baked enamel undercoats and should not interfere'with the action of the above solvent on nitrocellulose coatingsf It would be still better to use a wax-precipitating solvent which will not require the addition of any solvent depressant, that is.

such a solvent which has a fairly good solvent action on nitrocellulose coatings and which does not act upon baked enamel undercoats. Anhydrous methyl alcohol, which by itself is a good nitrocellulose solvent, will be more suitable than acetone.

Nitrocellulose lacquers and lacquer enamels are very sensitive to an change in the undercoat or in the surface t ereof, and will show a defect therein much more than would an ordinary oil paint, Consequently a finish re mover designed to remove only this kind of finish as astep in the refinishing) should preferably be completely ineflective towardsthe undercoat, in order to assure the absence of any, even the slightest, injury to the surface of the undercoat.

The following table gives illustrations of the action of various solvents on dried oil' paint. Tests were made by immersing a piece-of wood coated with a dried oil paint into a solvent and the action of the solvent .was noted. The comparative activity of solvents was represented by the number of seconds necessary to produce a wrinkling or blistering effect.

Ethyl acetate 105 In connection'with this table it should be mentioned that while benzol or solvent naphtha are comparatively slow solvents when used alone, they prove to be very active solvents in combination with other solvents, such as alcohols or ketones, and therefore they are unsuitable for use in any substantial proportion in carrying out the present invention.

Petroleum hydrocarbons on the other hand are true diluents because their admixture with solvents reduces the activity of the latter. This is illustrated by the activity (on oil paint) of some of the solvent mixtures (1: 1 by v( lume) given below:

Seconds Benzol and anhydrous methanol. Benzol and anhydrous ethanol 150 Benzol and acetone 65 Benzol and methyl acetate Light petroleum and anhydrous methanol 260 Light petroleum and anhydrous ethanol Almost no action (only softening) Light petroleum and acetone 280 Light petroleum and methyl acetate 110 In all examples given below the proportion of ingredients is given by volume, including the wax which is estimated in the molten state. It is understood that the formulas given in these examples should be regarded Ewample 1 P rts Light petroleum distillate (B. P. a

Anhydrous methanol 150 Paraffin wax 1 4 Ewample 2 Parts Petroleum ether (B. P. 10-60 C.) 50 Denatured alcohol Anhydrous acetone"; 25 Paraiiin wax 2 Ewample 3 Parts Carbon tetrachloride 50; Anhydrous methanol Paraffin wax 4;

Ewwmple 4 Parts Carbon tetrachloride 50 Anhydrous methanol 100 Nitrocellulose 2 Parafiin wax 3 Ewample'b' Parts Light petroleum distillate. (B. P. 60-

85 0.) 40 Denatured alcohol 40 Lugosol 20- Wax parafiin 2 In carying vout the process of removing the nitrocellulose lacquer, a remover such as one of the aboveformulas, is ap lied onto thecomposite coating having-un ercoat of baked enamel and one or a lurality of finish coatings of a nitrocell ose lacquer, the

remover being applied in a thin, preferably uniform, layer. It is then allowed to sta in contact with coating for a period of t1me, preferably not longer than is necessary to sufiiciently soften the upper coating. This time will depend on the particular formula of paint and varnish remover used, that is, upon the relative'c'utting speed of solvents included. With the formulas given above this time may be estimated about five to ten minutes.

After the upper, nitrocellulose lacquer coating has been thoroughly softened it is then scraped ofi with a rubber scraper, for example, or wiped oif with a piece of-rag.

It is advisable not to use any tools which could scratch or otherwise injure the undercoat. The upper coat removed, the undercoat of baked enamel is then carefully cleaned of remaining slight deposits of wax, by washing it with gasoline or a like wax solvent, and finally dried. Any breaks therein can be touched up with oil paint or asphalt paint and dried and is then ready for immediate application of a new top coating of nitrocellulose lacquer, one or several coats.

What I claim is:

A remover which is mild in character,

'capable of readily removing dried coats of nitrocellulose lacquer but being without substantial removing action on bakedenamel, such remover comprising wax, a wax solvent selected from the group consisting of petroleum distillates substantially all distilling below 85 (1., and carbon tetrachloride, and

a wax precipitant selected from the group consisting of acetone, methyl ethyl ketone, lugosol, mesityl oxide, methanol and denatured alcohol, the wax solvent being in amount less than the wax precipitant, and

, the total loosening solvent being less active on oil paints than is acetone alone.

In testimony whereof I afiix my signature.

BORIS N. LOUGOVOY. 

